Polymorph of a pharmaceutical

ABSTRACT

A new crystalline polymorph of ritonavir and methods for its use and preparation are disclosed.

This application is a divisional of U.S. Ser. No. 09/356,736 filed Jul.19, 1999, now U.S. Pat. No. 6,894,171 which claims the benefit of U.S.Provisional Application for Patent No. 60/093,432, filed Jul. 20, 1998and also claims the benefit of U.S. Provisional Application for PatentNo. 60/137,535, filed Jun. 4, 1999 from which priority is claimedpursuant to 35 U.S.C.§120 and which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

This invention relates to a novel crystalline polymorph of(2S,3S,5S)-5-(N-(N-((N-methyl-N-((2-isopropyl-4-thiazolyl)methyl)amino)carbonyl)-L-valinyl)amino)-2-(N-((5-thiazolyl)methoxycarbonyl)amino)-1,6-diphenyl-3-hydroxyhexane,methods for its preparation, methods for its use as a pharmaceuticalagent and pharmaceutical compositions comprising the novel crystallinepolymorph. This invention also relates to an amorphous form of(2S,3S,5S)-5-(N-(N-((N-methyl-N-((2-isopropyl-4-thiazolyl)methyl)amino)carbonyl)-L-valinyl)amino)-2-(N-((5-thiazolyl)methoxycarbonyl)amino)-1,6-diphenyl-3-hydroxyhexaneand methods for its preparation.

BACKGROUND OF THE INVENTION

Inhibitors of human immunodeficiency virus (HIV) protease have beenapproved for use in the treatment of HIV infection for several years. Aparticularly effective HIV protease inhibitor is(2S,3S,5S)-5-(N-(N-((N-methyl-N-((2-isopropyl-4-thiazolyl)methyl)amino)carbonyl)-L-valinyl)amino)-2-(N-((5-thiazolyl)methoxycarbonyl)amino)-1,6-diphenyl-3-hydroxyhexane(ritonavir), which is marketed as NORVIR®. Ritonavir is known to haveutility for the inhibition of HIV protease, the inhibition of HIVinfection, the inhibition of cytochrome P450 monooxygenase and theenhancement of the pharmacokinetics of compounds which are metabolizedby cytochrome P450 monooxygenase. Ritonavir is particularly effectivefor the inhibition of HIV infection when used alone or in combinationwith one or more reverse transcriptase inhibitors and/or one or moreother HIV protease inhibitors.

Ritonavir and processes for its preparation are disclosed in U.S. Pat.No. 5,541,206, issued Jul. 30, 1996. This patent discloses processes forpreparing ritonavir which produce a crystalline polymorph of ritonavirwhich is termed crystalline Form I. Substantially pure Form I has thepowder X-ray diffraction pattern, ¹³C solid state nuclear magneticresonance spectrum, the FT near infrared spectrum and the FT midinfrared spectrum which appear in FIGS. 1, 4, 6 and 8, respectively. Theangular positions (two theta) of the characteristic peaks in the powderX-ray diffraction pattern of substantially pure Form I shown in FIG. 1are 3.33°±0.1°, 6.76°±0.1°, 8.33°±0.1°, 14.61°±0.1°, 16.33°±0.1°,16.76°±0.1°, 17.03°±0.1°, 18.02°±0.1°, 18.62°±0.1°, 19.47°±0.1°,19.86°±0.1°, 20.25°±0.1°, 21.46°±0.1°, 23.46°±0.1° and 24.36°±0.1°.

Another process for the preparation of ritonavir is disclosed in U.S.Pat. No. 5,567,823, issued Oct. 22, 1996. The process disclosed in thispatent also produces ritonavir as crystalline Form I.

Pharmaceutical compositions comprising ritonavir or a pharmaceuticallyacceptable salt thereof are disclosed in U.S. Pat. No. 5,541,206, issuedJul. 30, 1996; U.S. Pat. No. 5,484,801, issued Jan. 16, 1996; U.S. Pat.No. 5,725,878, issued Mar. 10, 1998; and U.S. Pat. No. 5,559,158, issuedSep. 24, 1996 and in International Application No. WO98/22106, publishedMay 28, 1998 (corresponding to U.S. Ser. No. 08/966,495, filed Nov. 7,1997).

The use of ritonavir to inhibit an HIV infection is disclosed in U.S.Pat. No. 5,541,206, issued Jul. 30, 1996. The use of ritonavir incombination with one or more reverse transcriptase inhibitors to inhibitan HIV infection is disclosed in U.S. Pat. No. 5,635,523, issued Jun. 3,1997. The use of ritonavir in combination with one or more HIV proteaseinhibitors to inhibit an HIV infection is disclosed in U.S. Pat. No.5,674,882, issued Oct. 7, 1997. The use of ritonavir to inhibitcytochrome P450 monooxygenase and to enhance the pharmacokinetics ofcompounds metabolized by cytochrome P450 monooxygenase is disclosed inWO97/01349, published Jan. 16, 1997 (corresponding to U.S. Ser. No.08/687,774, filed Jun. 26, 1996).

It has now been unexpectedly discovered that ritonavir can be preparedas a new crystalline polymorph which is termed crystalline Form II.

All publications, issued patents and patent applications cited hereinare hereby incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the powder X-ray diffraction pattern of the substantially pureForm I crystalline polymorph of ritonavir.

FIG. 2 is the powder X-ray diffraction pattern of the substantially pureForm II crystalline polymorph of ritonavir.

FIG. 3 is the powder X-ray diffraction pattern of substantially pureamorphous ritonavir.

FIG. 4 is the 400 MHz solid state ¹³C nuclear magnetic resonancespectrum of the substantially pure Form I crystalline polymorph ofritonavir.

FIG. 5 is the 400 MHz solid state ¹³C nuclear magnetic resonancespectrum of the substantially pure Form II crystalline polymorph ofritonavir.

FIG. 6 is the FT near infrared spectrum of the substantially pure Form Icrystalline polymorph of ritonavir.

FIG. 7 is the FT near infrared spectrum of the substantially pure FormII crystalline polymorph of ritonavir.

FIG. 8 is the FT mid infrared spectrum of the substantially pure Form Icrystalline polymorph of ritonavir.

FIG. 9 is the FT mid infrared spectrum of the substantially pure Form IIcrystalline polymorph of ritonavir.

FIG. 10 is the differential scanning calorimetric thermogram forsubstantially pure amorphous ritonavir.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is a novel substantiallypure crystalline polymorph of(2S,3S,5S)-5-(N-(N-((N-methyl-N-((2-isopropyl-4-thiazolyl)methyl)amino)carbonyl)-L-valinyl)amino)-2-(N-((5-thiazolyl)methoxycarbonyl)amino)-1,6-diphenyl-3-hydroxyhexane(ritonavir). For the sake of identification, this crystalline polymorphis designated as the Form II crystalline polymorph of ritonavir.

Substantially pure Form II has the powder X-ray diffraction pattern, ¹³Csolid state nuclear magnetic resonance spectrum, the FT near infraredspectrum and the FT mid infrared spectrum which appear in FIGS. 2, 5, 7and 9, respectively. The two-theta angle positions of characteristicpeaks in the powder X-ray diffraction pattern of substantially pure FormII as shown in FIG. 2 are:

8.67°±0.1°, 9.88°±0.1°, 16.11°±0.1°, 16.70°±0.1°, 17.36°±0.1°,17.78°±0.1°, 18.40°±0.1°, 18.93°±0.1°, 20.07°±0.1°, 20.65°±0.1°,21.71°±0.1° and 25.38°±0.1°.

More preferably, substantially pure Form II is characterized by peaks inthe powder X-ray diffraction pattern having two-theta angle positions asshown in FIG. 2 of:

8.67°±0.1°, 9.51°±0.1°, 9.88°±0.1°, 10.97°±0.1°, 13.74°±0.1°,16.11°±0.1°, 16.70°±0.1°, 17.36°±0.1°, 17.78°±0.1°, 18.40°±0.1°,18.93°±0.1°, 19.52°±0.1°, 19.80°±0.1°, 20.07°±0.1°, 20.65°±0.1°,21.49°±0.1°, 21.71°±0.1°, 22.23°±0.1°, 25.38°±0.1°, 26.15°±0.1° and28.62°±0.1°.

The substantially pure Form II crystalline polymorph of ritonavir can beprepared from amorphous ritonavir by contacting amorphous ritonavir witha C1–C3 alcohol. The method of contacting may be either by saturatingthe amorphous compound in the solvent at ambient temperature and thenallowing the mixture to stand for an extended period of time (forexample, overnight) or by dissolving the amorphous compound in thesolvent at elevated temperature, preferably, at reflux, followed bycooling the solution to room temperature and isolating Form II.

In one embodiment of the process, the substantially pure Form IIcrystalline polymorph of ritonavir can be prepared from amorphousritonavir by preparing a saturated solution of amorphous ritonavir in aC1–C3 alcohol at room temperature and isolating Form II which results.In practice this can be accomplished by dissolving a sufficient amountof amorphous ritonavir in the C1–C3 alcohol at elevated temperature (upto reflux) such that when the solution is allowed to cool to roomtemperature a saturated solution is obtained, from which Form IIprecipitates and can be isolated. A preferred solvent for thepreparation of Form II is anhydrous ethanol. Isolation of the resultingsolid provides Form II.

Substantially pure amorphous ritonavir is prepared from the Form Icrystalline polymorph of ritonavir by melting Form I ritonavir andrapidly cooling the melt. Isolation of the resulting solid providesamorphous ritonavir.

Substantially pure amorphous ritonavir can also be prepared by slowlyadding a solution of ritonavir Form I in a suitable solvent (methylenechloride and the like; preferably, methylene chloride) at aconcentration of, preferably, about 1 g of ritonavir per about 1.5–2.0mL of solvent (preferably, about 1 g of ritonavir/about 1.5 mL ofmethylene chloride) to an anti-solvent (for example, hexane or heptaneand the like; preferably, hexane) at a concentration of about 60–110 mLof antisolvent/g of ritonavir; preferably, about 85–90 mL of hexane/g ofritonavir, followed by isolation (for example, by filtration) of theresulting solid.

Similarly, substantially pure amorphous ritonavir can also be preparedby slowly adding a solution of ritonavir Form I in a suitable solventsuch as methanol or the like at a concentration of, preferably, about 1g of ritonavir per about 1.5–2.0 mL of solvent (preferably, about 1 g ofritonavir/about 1.5 mL of methanol) to an anti-solvent such as methylt-butyl ether (MTBE) or the like at a concentration of about 60–150 mLof antisolvent/g of ritonavir, preferably, about 90–110 mL of MTBE/g ofritonavir and, most preferably, about 100 mL of MTBE/g of ritonavir,followed by isolation (for example, by filtration) of the resultingsolid.

Substantially pure amorphous ritonavir can also be prepared by slowlyadding a solution of ritonavir Form I in a suitable solvent (forexample, methanol and the like; preferably, methanol) at a concentrationof about 1 g of ritonavir per about 1.5–2.0 mL of solvent (preferably,about 1 g of ritonavir/about 1.6 mL of methanol) to water at about 0° C.at a concentration of about 400–500 mL of water/g of ritonavir(preferably, about 400 mL of water/g of ritonavir), followed byisolation (for example, by filtration) and drying of the resultingsolid.

Substantially pure amorphous ritonavir can also be prepared bylyophilization of a solution of ritonavir Form I. Preferred solvents areC1–C6 alcohols. A more preferred solvent is isobutanol.

Alternatively, in a preferred process, substantially pure Form II can beprepared by seeding a solution of ritonavir Form I in a suitable solvent(preferably, a C1–C3 alcohol; most preferably, ethanol) with undissolved(2S)-N-((1S)-1-Benzyl-2-((4S,5S)-4-benzyl-2-oxo-1,3-oxazolidin-5-yl)ethyl)-2-((((2-isopropyl-1,3-thiazol-4-yl)methyl)amino)-carbonyl)amino)-3-methylbutanamide.In a preferred method, ritonavir Form I is dissolved in ethanol(preferably, 200 proof ethanol) at a concentration of from about 150 g/Lto about 200 g/L, preferably, about 160 g/L. To the solution is addedseed crystals of(2S)-N-((1S)-1-Benzyl-2-((4S,5S)-4-benzyl-2-oxo-1,3-oxazolidin-5-yl)ethyl)-2-((((2-isopropyl-1,3-thiazol-4-yl)methyl)amino)carbonyl)-amino)-3-methylbutanamidein the amount of from about 0.02 g to about 0.10 g of seed crystals/g ofritonavir. The amount of seed crystals added is such that it exceeds thesaturation amount in the solvent being used so that there areundissolved seed crystals present in the ritonavir solution. The mixtureis allowed to stand at a temperature of from about 0° C. to about 15° C.(preferably, about 5° C.) for from about 12 hours to about 48 hours(preferably, about 24 hours). The resulting crystalline ritonavir FormII is isolated by filtration.

In yet another preferred alternative method, substantially pure Form IIcan be prepared by recrystallization of Form I or mixtures of Form I andForm II from a solution in a suitable solvent (for example, ethylacetate or isopropyl acetate or chloroform and the like other solventswith like dielectric constant; preferably, ethyl acetate), with seedingwith Form II crystals, followed by addition of an anti-solvent (forexample, heptane, hexane, toluene, petroleum ether and the like otheranti-solvents with like dielectric constant; preferably, heptane). Theamount of seed crystals added is such that it exceeds the saturationamount in the solvent being used so that there are undissolved seedcrystals present in the ritonavir solution. In a preferred method,ritonavir (Form I or a mixture of Form I and Form II) is dissolved inethyl acetate (from about 4.0 L to about 6.0 L/kg of ritonavir) withheating (at from about 65° C. to about 70° C.). The solution is slowlycooled to from about 55° C. to about 50° C., preferably about 52° C.Seed crystals of ritonavir Form II (from about 0.5 g of Form II seedcrystals/kg of ritonavir to about 10.0 g of Form II seed crystals/kg ofritonavir, preferably about 1.25 g of Form II seed crystals/kg ofritonavir) are added and the mixture is stirred for about 1 hour at atemperature of from about 55° C. to about 50° C., preferably about 52°C. The amount of seed crystals added is such that it exceeds thesaturation amount in the solvent being used so that there areundissolved seed crystals present in the ritonavir solution. Heptane(from about 1.0 L/kg of ritonavir to about 4.0 L/kg of ritonavir;preferably, about 2.8 L/kg of ritonavir) is added with mixing and themixture is allowed to slowly cool to about 25° C. and is then stirredfor at least 12 hours at about 25° C. The product is isolated byfiltration/centrifugation and is dried under vacuum with heating. On amanufacturing scale (300–400 kg batches), it has been observed thatisolation by filtration/centrifugation is considerably faster for FormII than for the corresponding amount of Form I (16 hours versus 24–30hours).

It has also been found that Form II or mixtures of Form II and Form Ican be converted to substantially pure Form I by dissolving the Form IIor mixture of Form II and Form I in a suitable solvent (for example,ethyl acetate or isopropyl acetate and the like; preferably, ethylacetate) at a concentration of about 1 kg of ritonavir/4 L of solvent(preferably, ethyl acetate) with heating. The hot solution of ritonaviris slowly added (preferably, through a filter) to a slurry of seedcrystals of ritonavir Form I (from about 0.5% to about 10% by weightrelative to amount of ritonavir Form II or mixture of Form II and FormI; preferably, from about 0.5% to about 5% by weight and, mostpreferably, from about 0.5% to about 1% by weight) in an anti-solvent(for example, heptane or hexane and the like; preferably, heptane) at aconcentration of about 1 kg of ritonavir (Form II or mixture of Form IIand Form I) per about 4–8 L of antisolvent (preferably, about 1 kg ofritonavir (Form II or mixture of Form II and Form I)/about 4 L ofheptane). The mixture is cooled to about 20° C. and stirred for at least3 hours. Isolation (for example, by filtration) and drying of theresulting solid provides ritonavir Form I.

The following examples will serve to further illustrate the preparationof the novel forms of ritonavir of the invention and the conversion ofForm II to Form I.

EXAMPLE 1 Preparation of Amorphous Ritonavir

Form I crystalline polymorph of ritonavir (100 g) was melted at 125° C.by heating Form I. The melt was maintained at a temperature of 125° C.for 3 hours. The melt was rapidly cooled by placing the containerholding the melt into a Dewar flask containing liquid nitrogen. Theresulting glass was ground with a mortar and pestle to provide amorphousritonavir (100 g). Powder X-ray diffraction analysis confirmed that theproduct was amorphous. Differential scanning calorimetric analysisdetermined that the glass transition point was from about 45° C. toabout 49° C. (Measured onset at 45.4° C. and which ends at 49.08° C.,with a midpoint of 48.99° C.).

EXAMPLE 2 Preparation of Crystalline Ritonavir (Form II)

Amorphous ritonavir (40.0 g) was dissolved in boiling anhydrous ethanol(100 mL). Upon allowing this solution to cool to room temperature, asaturated solution was obtained. After standing overnight at roomtemperature, the resulting solid was isolated from the mixture byfiltration and was air dried to provide Form II (approximately 24.0 g).

EXAMPLE 3 Preparation of(2S)-N-((1S)-1-Benzyl-2-((4S,5S)-4-benzyl-2-oxo-1,3-oxazolidin-5-yl)ethyl)-2-((((2-isopropyl-1,3-thiazol-4-yl)methyl)amino)carbonyl)amino)-3-methylbutanamideEXAMPLE 3a Preparation of(4S,5S)-5-((2S)-2-t-butyloxycarbonylamino-3-phenylpropyl)-4-benzyl-1,3-oxazolidin-2-one

(2S,3S,5S)-2-Amino-3-hydroxy-5-t-butyloxycarbonylamino-1,6-diphenylhexanesuccinate salt (30 g, 63 mmol; U.S. Pat. No. 5,654,466),((5-thiazolyl)methyl)-(4-nitrophenyl)carbonate hydrochloride (22.2 g;U.S. Pat. No. 5,597,926) and sodium bicarbonate (16.2 g) were mixed with300 mL of water and 300 mL of ethyl acetate and the mixture was stirredat room temperature for about 30 minutes. The organic layer was thenseparated and heated at about 60° C. for 12 hours, and then stirred at20–25° C. for 6 hours. 3 mL of ammonium hydroxide (29% ammonia in water)was added and the mixture stirred for 1.5 hours. The resulting mixturewas washed with 4×200 mL of 10% aqueous potassium carbonate and theorganic layer was separated and evaporated under vacuum to provide anoil. The oil was suspended in about 250 mL of heptane. The heptane wasevaporated under vacuum to provide a yellow solid. The yellow solid wasdissolved in 300 mL of THF and 25 mL of 10% aqueous sodium hydroxide wasadded. After stirring for about 3 hours, the mixture was adjusted to pH7 by addition of 4N HCl (about 16 mL). The THF was evaporated undervacuum to leave an aqueous residue, to which was added 300 mL ofdistilled water. After stirring this mixture, a fine suspension ofsolids resulted. The solid was collected by filtration and the filteredsolid was washed with water (1400 mL) in several portions, resulting inthe desired product.

EXAMPLE 3b Preparation of(4S,5S)-5-((2S)-2-amino-3-phenylpropyl)-4-benzyl-1,3-oxazolidin-2-one

The crude, wet product of Example 3a was slurried in 1N HCl (192 mL) andthe slurry was heated to 70° C. with stirring. After 1 hour, THF (100mL) was added and stirring at 65° C. was continued for 4 hours. Themixture was then allowed to cool to 20–25° C. and was stirred overnightat 20–25° C. The THF was removed by evaporation under vacuum and theresulting aqueous solution was cooled to about 5° C., causing someprecipitation to occur. The aqueous mixture was adjusted to pH 7 byaddition of 50% aqueous sodium hydroxide (about 18.3 g). The resultingmixture was extracted with ethyl acetate (2×100 mL) at about 15° C. Thecombined organic extracts were washed with 100 mL of brine and theorganic layer was separated and stirred with sodium sulfate (5 g) andDarco G-60 (3 g). This mixture was warmed on a hot plate for 1 hour at45° C. The hot mixture was then filtered through a bed of diatomaceousearth and the filter pad was washed with ethyl acetate (100 mL). Thefiltrate was evaporated under vacuum to provide an oil. The oil wasredissolved in methylene chloride (300 mL) and the solvent wasevaporated under vacuum. The resulting oil was dried at room temperatureunder vacuum to provide the desired product (18.4 g) as a glassy syrup.

EXAMPLE 3c Preparation of(2S)-N-((1S)-1-Benzyl-2-((4S,5S)-4-benzyl-2-oxo-1,3-oxazolidin-5-yl)ethyl)-2-((((2-isopropyl-1,3-thiazol-4-yl)methyl)amino)carbonyl)amino)-3-methylbutanamide

N-((N-Methyl-N((2-isopropyl-4-thiazolyl)methyl)amino)carbonyl)-L-valine(10.6 g, 33.9 mmol; U.S. Pat. No. 5,539,122 and International PatentApplication No. WO98/00410), the product of Example 3b (10.0 g, 32.2mmol) and 1-hydroxybenzotriazole (5.2 g, 34 mmol) were dissolved in THF(200 mL). 1,3-dicylcohexylcarbodiimide (DCC, 7.0 g, 34 mmol) was thenadded to the THF mixture and the mixture was stirred at 22° C. for 4hours. Citric acid (25 mL of 10% aqueous solution) was added andstirring continued for 30 minutes. The THF was then evaporated undervacuum. The residue was dissolved in ethyl acetate (250 mL) and washedwith 10% citric acid solution (175 mL). NaCl (5 g) was added toaccelerate the separation of the layers. The organic layer wassequentially washed with 10% aq. sodium carbonate (2×200 mL) and water(200 mL). The organic layer was then dried over sodium sulfate (20 g),filtered and evaporated under vacuum. The resulting product (20.7 g of afoam) was dissolved in hot ethyl acetate (150 mL) and then heptane (75mL) was added. Upon cooling, another 75 mL of heptane was added and themixture was heated to reflux. Upon cooling to room temperature, noprecipitate formed. The solvents were evaporated under vacuum and theresidue was redissolved in a mixture of 200 mL ethyl acetate/100 mLheptane. The small amount of undissolved solid was removed byfiltration. The filtrate was evaporated under vacuum and the residue wasdissolved in a mixture of 100 mL ethyl acetate/50 mL heptane, giving aclear solution. The solution was cooled to −10° C. and a whiteprecipitate formed. The mixture was allowed to sit at −15° C. for 24hours. The resulting solid was collected by filtration, washed with 1:1ethyl acetate/heptane (2×24 mL) and dried in a vacuum oven at 55° C. toprovide the desired product as a beige solid (16.4 g).

¹H NMR (DMSO-d₆) δ 7.84 (1H, doublet J=8.6), 7.71 (1H, singlet),7.32–7.11 (11H, multiplet), 6.09 (1H, doublet J=8.5), 4.51 (1H ABJ=16.2), 4.43 (1H AB J=16.2), 4.22 (1H, multiplet), 4.07 (1H,multiplet), 3.96 (1H, doublet of doublet J=7.3,7.4), 3.65 (1H,multiplet), 3.23 (1H, septuplet J=6.9), 2.89 (3H, singlet), 2.84–2.60(4H, multiplet), 1.94 (1H, multiplet), 1.76–1.49 (2H, multiplet), 1.30(6H, doublet J=6.9), 0.80 (3H, doublet J=5.8), 0.77 (3H, doublet J=5.8)¹³C NMR (DMSO-d₆) δ 177.2, 171.5, 157.6, 157.5, 152.8, 138.3, 136.5,129.5, 129.2, 128.2, 128.0, 126.4, 126.0, 114.0, 77.2, 59.9, 57.6, 48.2,46.2, 40.4, 40.1, 39.1, 34.5, 32.4, 30.3, 22.8, 22.8, 19.4, 18.3.

EXAMPLE 4 Preparation of Crystalline Ritonavir (Form II)

To a solution of 1.595 g of ritonavir Form I in 10 mL of 200 proofethanol was added an amount of the product of Example 3c (approximately50 micrograms) such that all of the added amount of the product ofExample 3c did not dissolve. This mixture was allowed to stand at about5° C. for 24 hours. The resulting crystals were isolated by filtrationthrough 0.45 micron nylon filter and air dried to provide ritonavir FormII.

EXAMPLE 5 Alternative Preparation of Crystalline Ritonavir (Form II)

Ethyl acetate (6.0 L/kg of ritonavir) was added to ritonavir (Form I ora mixture of Form I and Form II) in a reaction vessel. The mixture wasstirred and heated to 70° C. until all solids were dissolved. Thesolution was filtered (utilizing a centrifuge pump and 5×20 inchcartridge filters having a porosity of 1.2 microns) and the filtrate wasallowed to cool to 52° C. at a rate of 2–10° C./hour. To this solutionwas added an amount of ritonavir Form II seed crystals (about 1.25 g ofForm II seed crystals/kg of ritonavir) such that all of the seedcrystals did not dissolve and the mixture was stirred at 52° C. for notless than 1 hour at an agitation rate of 15 RPM. The mixture was thenallowed to cool to 40° C. at a rate of 10° C./hour. Heptane (2.8 L/kg ofritonavir) was added at a rate of 7 L/minute with mixing. The mixturewas allowed to cool to 25° C. at a rate of 10° C./hour with mixing. Thenthe mixture was stirred for not less than 12 hours at 25° C. The productwas isolated by filtration using a Heinkel type centrifuge (run timeapproximately 16 hours). The product was dried at 55° C. under vacuum(50 mm Hg) for 16–25 hours to provide ritonavir crystal Form II.

EXAMPLE 6 Preparation of Amorphous Ritonavir

Ritonavir Form I (40 g) was dissolved in methylene chloride (60 mL).This solution was slowly added over 15 minutes to a round bottom flaskequipped with an overhead stirrer and containing hexanes (3.5 L). Theresulting slurry was allowed to stir for 10 minutes. The precipitate wasfiltered and dried at room temperature in a vacuum oven to provideamorphous ritonavir (40 g).

EXAMPLE 7 Preparation of Amorphous Ritonavir

Ritonavir Form I (5 g) was dissolved in methanol (8 mL). This solutionwas slowly added to a round bottom flask equipped with an overheadstirrer and containing distilled water (2 L), while maintaining theinternal temperature near 0° C. The resulting solid was filtered to givea sticky solid which was dried in a vacuum oven at 20–25° C. for 12–18hours to give amorphous ritonavir (2.5 g).

EXAMPLE 8 Preparation of Ritonavir Form I

Ritonavir Form II (1 kg) was added to a reactor (A), followed by theaddition of ethyl acetate (4 L). This mixture was refluxed until all ofthe solids were dissolved.

To a separate reactor (B) was added an amount of seed crystals ofritonavir Form I (5 g), followed by the addition of heptane (4 L), suchthat all of the seed crystals did not dissolve. This mixture (a slurry)was stirred at 23° C.±5° C.

The hot solution from reactor A was slowly filtered, using a 0.2 micronfilter cartridge, into the mixture in reactor B over not less than 2hours. The resulting slurry in reactor B was cooled to 20° C. andstirred for not less than 3 hours. The resulting slurry was filtered,the filtered solid washed with heptane and then dried in a vacuum ovenat 65° C. to provide ritonavir Form I.

A preferred pharmaceutical composition comprising ritonavir, especially,ritonavir Form II, has the following composition, encapsulated in a softelastic gelatin capsule.

Ritonavir Form II  100.0 mg Ethanol, dehydrated  120.0 mg Oleic acid709.75 mg Butylated hydroxytoluene  0.25 mg Polyoxyl 35 castor oil  60.0mg (Cremophor EL ®) Water  10.0 mg

The preferred composition can be prepared according to the followingmethod.

The following protocol is employed in the preparation of 1000 softgelatin capsules:

Scale Amount (mg/capsule) Name (g) Q.S. Nitrogen, N.F. Q.S. 118.0Ethanol, 118.0 dehydrated, USP, 200 Proof 2.0 Ethanol, 2.0 dehydrated,USP, 200 Proof 0.25 Butylated Hydroxytoluene, NF 0.25 704.75 Oleic Acid,NF 704.75 100.0 Ritonavir Form II 100.0 10.0 Water, purified, USP(distilled) 10.0 60.0 Polyoxyl 35 Castor Oil, NF 60.0 5.000 Oleic Acid,NF 5.000

A mixing tank and suitable container are purged with nitrogen. 118.0 gof ethanol is weighed, blanketed with nitrogen, and held for later use.The second aliquot of ethanol (2 g) is then weighed, and mixed with 0.25g of butylated hydroxytoluene until clear. The mixture is blanketed withnitrogen and held. The main mixing tank is heated to 28° C. (not toexceed 30° C.). 704.75 g of oleic acid is then charged into the mixingtank. 100.0 g of ritonavir Form II is then added to the oleic acid withmixing. The ethanol/butylated hydroxytoluene is then added to the mixingtank, followed by the 118.0 g of ethanol measured previously, and mixedfor at least 10 minutes. 10 g of water is then charged into the tank andmixed until the solution is clear (for not less than 30 minutes). 60.0 gof Polyoxyl 35 castor oil is charged into the tank and mixed untiluniform. The solution is stored at 2–8° C. until encapsulation.According to the procedures described in International PatentApplication WO98/22106, 1.0 g of the solution is filled into each softgelatin capsule and the soft gelatin capsules are then dried, and storedat 2–8° C.

As used herein, the term “substantially pure”, when used in reference toa polymorph of ritonavir, refers to a polymorph of ritonavir, Form I orForm II, which is greater than about 90% pure. This means that thepolymorph of ritonavir does not contain more than about 10% of any othercompound and, in particular, does not contain more than about 10% of anyother form of ritonavir. More preferably, the term “substantially pure”refers to a polymorph of ritonavir, Form I or Form II, which is greaterthan about 95% pure. This means that the polymorph of ritonavir does notcontain more than about 5% of any other compound and, in particular,does not contain more than about 5% of any other form of ritonavir. Evenmore preferably, the term “substantially pure” refers to a polymorph ofritonavir, Form I or Form II, which is greater than about 97% pure. Thismeans that the polymorph of ritonavir does not contain more than about3% of any other compound and, in particular, does not contain more thanabout 3% of any other form of ritonavir.

As used herein, the term “substantially pure”, when used in reference toamorphous ritonavir, refers to amorphous ritonavir which is greater thanabout 90% pure. This means that the amorphous ritonavir does not containmore than about 10% of any other compound and, in particular, does notcontain more than about 10% of any other form of ritonavir. Morepreferably, the term “substantially pure”, when used in reference toamorphous ritonavir, refers to amorphous ritonavir which is greater thanabout 95% pure. This means that the amorphous ritonavir does not containmore than about 5% of any other compound and, in particular, does notcontain more than about 5% of any other form of ritonavir. Even morepreferably, the term “substantially pure”, when used in reference toamorphous ritonavir, refers to amorphous ritonavir which is greater thanabout 97% pure. This means that the amorphous ritonavir does not containmore than about 3% of any other compound and, in particular, does notcontain more than about 3% of any other form of ritonavir.

Powder X-ray diffraction analysis of samples was conducted in thefollowing manner. Samples for X-ray diffraction analysis were preparedby spreading the sample powder (with no prior grinding required) in athin layer on the sample holder and gently flattening the sample with amicroscope slide. A Nicolet 12/V X-ray Diffraction System was used withthe following parameters: X-ray source: Cu-Kα1; Range: 2.00–40.00° TwoTheta; Scan Rate: 1.00 degree/minute; Step Size: 0.02 degrees;Wavelength: 1.540562 angstroms.

Characteristic powder X-ray diffraction pattern peak positions arereported for polymorphs in terms of the angular positions (two theta)with an allowable variability of ±0.1°. This allowable variability isspecified by the U.S. Pharmacopeia, pages 1843–1844 (1995). Thevariability of ±0.1° is intended to be used when comparing two powderX-ray diffraction patterns. In practice, if a diffraction pattern peakfrom one pattern is assigned a range of angular positions (two theta)which is the measured peak position ±0.1° and a diffraction pattern peakfrom the other pattern is assigned a range of angular positions (twotheta) which is the measured peak position ±0.1° and if those ranges ofpeak positions overlap, then the two peaks are considered to have thesame angular position (two theta). For example, if a diffraction patternpeak from one pattern is determined to have a peak position of 5.20°,for comparison purposes the allowable variability allows the peak to beassigned a position in the range of 5.10°–5.30°. If a comparison peakfrom the other diffraction pattern is determined to have a peak positionof 5.35°, for comparison purposes the allowable variability allows thepeak to be assigned a position in the range of 5.25°–5.45°. Becausethere is overlap between the two ranges of peak positions (i.e.,5.10°–5.30° and 5.25°–5.45°) the two peaks being compared are consideredto have the same angular position (two theta).

Solid state nuclear magnetic resonance analysis of samples was conductedin the following manner. A Bruker AMX-400 MHz instrument was used withthe following parameters: CP-MAS (cross-polarized magic angle spinning);spectrometer frequency for ¹³C was 100.627952576 MHz; pulse sequence wascp2lev; contact time was 2.5 milliseconds; temperature was 27.0° C.;spin rate was 7000 Hz; relaxation delay was 6.000 sec; 1^(st) pulsewidth was 3.8 microseconds; 2^(nd) pulse width was 8.6 microseconds;acquisition time was 0.034 seconds; sweep width was 30303.0 Hz; 2000scans.

FT near infrared analysis of samples was conducted in the followingmanner. Samples were analyzed as neat, undiluted powders contained in aclear glass 1 dram vial. A Nicolet Magna System 750 FT-IR spectrometerwith a Nicolet SabIR near infrared fiber optic probe accessory was usedwith the following parameters: the source was white light; the detectorwas PbS; the beamsplitter was CaF2; sample spacing was 1.0000; digitizerbits was 20; mirror velocity was 0.3165; the aperture was 50.00; samplegain was 1.0; the high pass filter was 200.0000; the low pass filter was11000.0000; the number of sample scans was 64; the collection length was75.9 seconds; the resolution was 8.000; the number of scan points was8480; the number of FFT points was 8192; the laser frequency was 15798.0cm−1; the interferogram peak position was 4096; the apodization wasHapp-Genzel; the number of background scans was 64 and the backgroundgain was 1.0.

FT mid infrared analysis of samples was conducted in the followingmanner. Samples were analyzed as neat, undiluted powders. A NicoletMagna System 750 FT-IR spectrometer with a Spectra-Tech InspectIR videomicroanalysis accessory and a Germanium attenuated total reflectance (GeATR) crystal was used with the following parameters: the source wasinfrared; the detector was MCT/A; the beamsplitter was KBr; samplespacing was 2.0000; digitizer bits was 20; mirror velocity was 1.8988;the aperture was 100.00; sample gain was 1.0; the high pass filter was200.0000; the low pass filter was 20000.0000; the number of sample scanswas 128; the collection length was 79.9 seconds; the resolution was4.000; the number of scan points was 8480; the number of FFT points was8192; the laser frequency was 15798.0 cm−1; the interferogram peakposition was 4096; the apodization was triangular; the number ofbackground scans was 128 and the background gain was 1.0.

Differential scanning calorimetric analysis of samples was conducted inthe following manner. A T.A. Instruments Thermal Analyzer 3100 withDifferential Scanning Calorimetry module 2910 was used, along withModulated DSC software version 1.1A. The analysis parameters were:Sample weight: 2.28 mg, placed in a covered, uncrimped aluminum pan;Heating rate: room temperature to 150° C. at 5° C./minute under anitrogen purge.

The foregoing is merely illustrative of the invention and is notintended to limit the invention to the disclosed embodiments. Variationsand changes which are obvious to one skilled in the art are intended tobe within the scope and nature of the invention which are defined in theappended claims.

1. A process for preparing amorphous ritonavir, comprising adding asolution of ritonavir to a sufficient amount of an anti-solvent, therebyproducing solid amorphous ritonavir, wherein said solution comprises asolvent selected from the group consisting of methylene chloride andmethanol.
 2. The process of claim 1, wherein said solution comprisesmethylene chloride as a solvent, and the relative amount of saidanti-solvent as compared to ritonavir in said solution is about 60–110mL of anti-solvent per gram of ritonavir.
 3. The process of claim 1,wherein said solution comprises methylene chloride as a solvent, andsaid anti-solvent is hexane, and wherein the concentration of ritonavirin said solution is about 1 gram of ritonavir per about 1.5 mL ofmethylene chloride, and the relative amount of said anti-solvent ascompared to ritonavir in said solution is about 85–90 mL of anti-solventper gram of ritonavir.
 4. The process of claim 1, wherein said solutioncomprises methanol as a solvent, and the relative amount of saidanti-solvent as compared to ritonavir in said solution is about 60–150mL of anti-solvent per gram of ritonavir.
 5. The process of claim 1,wherein said solution comprises methanol as a solvent, and saidanti-solvent is methyl t-butyl ether, and wherein the concentration ofritonavir in said solution is about 1 g of ritonavir per 1.5 mL ofmethanol, and the relative amount of said anti-solvent as compared toritonavir in said solution is about 90–110 mL of anti-solvent per gramof ritonavir.
 6. The process of claim 1, wherein said solution comprisesmethanol as a solvent, and said anti-solvent is methyl t-butyl ether,and wherein the concentration of ritonavir in said solution is about 1 gof ritonavir per 1.5 mL of methanol, and the relative amount of saidanti-solvent as compared to ritonavir in said solution is about 100 mLof anti-solvent per gram of ritonavir.
 7. A process for preparingsubstantially pure amorphous ritonavir, comprising adding a solution ofritonavir to a sufficient amount of an anti-solvent, thereby producingsubstantially pure solid amorphous ritonavir, wherein said solutioncomprises methylene chloride as a solvent, and said anti-solvent isselected from the group consisting of hexane and heptane, and whereinthe concentration of ritonavir in said solution is about 1 gram ofritonavir per about 1.5–2.0 mL of methylene chloride, and the relativeamount of said anti-solvent as compared to ritonavir in said solution isabout 60–110 mL of anti-solvent per gram of ritonavir.
 8. A process forpreparing substantially pure amorphous ritonavir, comprising adding asolution of ritonavir to a sufficient amount of an anti-solvent, therebyproducing substantially pure solid amorphous ritonavir, wherein saidsolution comprises methanol as a solvent, and said anti-solvent ismethyl t-butyl ether.
 9. The process of claim 8, wherein theconcentration of ritonavir in said solution is about 1 gram of ritonavirper about 1.5–2.0 mL of methanol, and the relative amount of saidanti-solvent as compared to ritonavir in said solution is about 60–150mL of anti-solvent per gram of ritonavir.
 10. The process of claim 8,wherein the concentration of ritonavir in said solution is about 1 gramof ritonavir per about 1.5 mL of methanol, and the relative amount ofsaid anti-solvent as compared to ritonavir in said solution is about90–110 mL of anti-solvent per gram of ritonavir.